Ductile iridium alloy



United States Patent Ofi 3,293,031 Patented Dec. 20, 1966 ice 3,293,031 DUCTILE IRIDIUM ALLOY David W. Rhys, Honnslow, England, and Peter C. Cresswell, Los Angeles, Calif., assignors to The International Nickel Company, Inc., New York, N .Y., a corporation of Delaware No Drawing. Filed Nov. 27, 1964, Ser. No. 414,427 Claims priority, application Great Britain, Dec. 23, 1963, 50,767 63 6 Claims. (Cl. 75-172) The present invention relates to iridium alloys and, more particularly, to production of wrought products made of iridium alloys.

It is well known that iridium when produced in sheet or strip form by methods in the prior art is brittle and cannot readily be bent. For example, commercially pure iridium strip 0.02 inch thick cannot withstand, without cracking, being bent around a lesser radius than about inch. Iridium sheet also is not very strong. Sheet of pure iridium in the as-rolled condition has a strength of about 10 long tons per square inch (t.s.i.) in a tensile test at room temperature. Moreover, iridium sheet, because of its lack of ductility, does not readily give a clean edge when sheared and this fact is disadvantageous for the production of a sound butt-weld. The weld is usually made along the abutted edges of the sheet with a tungsten arc and the iridium cracks severely in the heat-affected zone.

Although many attempts were made to overcome the foregoing difiiculties and other difliculties and disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on in industrial scale.

It has now been discovered that high iridium alloy (at least 97.5% iridium) wrought products characterized by tensile strength, ductility and weldability which are greatly improved over the corresponding characteristics of pure iridium can be made of a new iridium alloy.

It is an object of the present invention to provide a new iridium alloy;

It is a further object of the invention to provide a new high iridium alloy wrought product of sheet, strip, wire and the like made of a new iridium all-y.

Other objects and advantages of the invention will become apparent from the following description.

Generally speaking, the present invention contemplates a new iridium alloy containing about 0.1% to about 0.5 metal from the group consisting of titanium and zirconium with the balance essentially iridium and characterized by high tensile strength, ductility and weldability. Advantageously, for good workability, the alloy contains less than 0.5% zirconium, e.g., 0.1% to 0.3% zirconium, and for making wrought products the invention provides, as a specially advantageous embodiment thereof, an advantageously workable high iridium alloy containing about 0.1 to about 0.5% of metal from the group consisting of about 0.1% to about 0.5% titanium and about 0.1% to about 0.3% zirconium with balance iridium. The wrought product of the invention includes sheet, strip, rod and wire made of the aforesaid advantageously workable iridium alloy of the invention.

While the balance of the alloy of the invention is referred to as essentially iridium, it is to be understood that herein balance essentially iridium does not exclude small amounts, totaling not more than about 2%, of impurities and incidental elements which do not affect the basic and novel characteristics of the alloy. For instance, the alloy of the invention can contain up to about 0.5% palladium, up to about 0.5 platinum or up to about 0.5 of each of rhodium, iron and nickel. In order to obtain good characteristics of tensile strength, ductility and weldability in accordance with the invention, it is particularly important that the alloy must not contain more than about 0.05% lead, 0.05% gold, 0.05% silver or 0.05% bismuth, which elements are especially detrimental impurities In any event, the alloy of the inven- 5 tion contains at least about 97.5% iridium.

The alloy of the invention is a single phase alloy and the advantageously workable alloy is characterized by good workability in the cast condition at temperatures from about 1500 C. to about 2200 C. Once the metal has been forged, working at lower temperatures is possible and the heavily worked alloy is readily worked at room temperature. Dual phase iridium alloys, e.g., iridium alloys containing more than about 0.5 titanium and/or zirconium, are to be avoided in order to obtain good characteristics of workability and ductility in accordance with the invention.

It has been surprisingly found that the alloy of the invention is characterized by a recrystallization temperature of about 1200 C. to about 1300 C., in contrast to the recrystallization temperature of 800 C. of pure iridium. The high recrystallization tmeperature of the alloy of the invention enables the alloy to retain a fibrous structure while being rolled into sheet and this fibrous structure enables rolled sheet of the' alloy of the invention to be sheared to give a good edge.

In carrying the invention into practice, it is advantageous that the alloy of the invention contain about 0.1% to about 0.3% titanium, about 0.2% to about 0.3% zirconium with the total percentage of titanium plus zirconium not exceeding about 0.5 and with the balance essentially iridium since when of this advantageous composition, the alloy has particularly good ductility.

For the purpose of giving those skilled in the art a better understanding of the invention and a better appreciation of the advantages of the invention, the following illustrative examples are given.

Examples of alloy compositions (Alloys A, B, C, D and E) in accordance with the invention are set forth in Table I. Also, Table I shows the composition of two alloys, Alloys X and Y, which are not in accordance with the invention.

TABLE I Alloy Ti Zr Pd Pt Fe Ir Percent Percent Percent Percent Percent A 0.1 0.01 0.01 0.005 Bal. 0. 01 0. 01 0. 010 1331. C 0. 01 0. 01 0. 015 Bal. 0. 01 0. 01 0. 015 Bal. 0. 01 0. 01 0. 010 Ba]. Bal. Bal.

Ingots of Alloys A through E and Alloys X and Y were produced by melting iridium in a zirconia crucible in an atmosphere of argon, then adding to it a sintered compact of mixed iridium and zirconium or titanium powder containing the requisite amount of the alloying element and re-melting the metal. The aforeaid ingots of Alloys A through E were successfully worked into sheet by the following procedure: The ingots were heated in hydrogen to 1500 C. to 1600 C. and were forged to 25% reduction in area; they were then hot rolled at 1500 C. to 0.1 inch thickness by'reductions of 0.015 inch per pass and were finally rolled to 0.02 inch thickness at 800 C. with reductions of 0.003 inch per pass. When attempts were made to work the ingots of Alloys X and Y, which were two-phase alloys, the metal of the ingots broke up and could not be worked into sheet. Sheets of each of Alloys A, B, C, D and E were successfully butt-welded with a tungsten arc and the weld specimens were subsequently bent around a one-quarter inch radius without. cracking.

Sheet of Alloy C containing 0.5% titanium had a strength of about 88 long tons per square inch in the as-rolled condition. After being welded, sheet of Alloys A, B, C, D and E had a strength of about t.s.i. to about 16 t.s.i. across the weld whereas commercially pure iridium when welded has a strength about 7 t.s.i. across the weld. A typical analysis of commercially pure iridium sheet is 0.02% platinum, 0.04% palladium, 0.03% rhodium, 0.0001% lead, 0.05% 'iron, 0.001% nickel, less than 0.005% titanium, less than 0.005% zirconium and balance iridium. All percentage compositions set forth herein are by weight. The welded sheet made of the alloy of the invention was sound in the heat-affected zone.

' Results of tensile tests of sheet in accordance with the invention are set forth in Table I1 hereinafter.

TABLE II Unwelded Sheet Welded Sheet U.T.S. (t.s.i.):Ultimate tensile strength in long tons per square inch The unwelded sheet referred to in Table II was tested in the condition obtained by the final rolling treatment at 800 C. The welded sheet was tested with the tensile stress exerted across the weld and the specimens fractured within the heat-affected zone.

As a further example of the invention, an iridium alloy was made containing about 0.3% titanium, about 0.2% zirconium and balance essentially iridium. The alloy was melted and cast into an ingot and the ingot was thereafter forged and rolled into high iridium alloy sheet which was both ductile and weldable.

The iridium alloy of the invention is characterized by a minimum ultimate tensile strength of at least about 28 t.s.i. at room temperature when in the condition obtained by rolling at about 800 C. Also, iridium alloy sheet in accordance with the invention and when in the immediately aforesaid condition is characterized by a level of ductility that is sufficient to enable sheet about 0.02 inch thick to be bent without cracking around a radius of about three-eighths of an inch or greater.

The present invention is particularly applicable to production of iridium alloy sheet, strip, rod and wire which are useful for making crucibles, springs, electrodes for spark plugs, and similar devices for use at elevated temperature.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An iridium alloy consisting essentially of about 0.1% to about 0.5% metal from the group consisting of titanium and zirconium with balance essentially iridium.

2. An iridium alloy consisting essentially of about 0.1% to about 0.5% of metal from the group consisting of about 0.1% to about 0.5% titanium and about 0.1% to about 0.3% zirconium with balance essentially iridium.

3. An iridium alloy consisting essentially of about 0.1% to about 0.3% titanium, about 0.2% to about 0.3% zirconium with the total percentage of titanium plus zirconium not exceeding about 0.5 and with the balance essentially iridium.

4. Wrought iridium alloy sheet, strip, rod, wire and the like made of an alloy consisting essentially of about 0.1% to about 0.5% metal from the group consisting of about 0.1% to about 0.5% titanium and about 0.1% to about 0.3% zirconium with balance essentially iridium.

5. Wrought iridium alloy sheet, strip, rod, wire and the like made of an alloy consisting essentially of about 0.1% to about 0.3% titanium, about 0.2% to about 0.3% zirconium with the total percentage of titanium plus zirconium not exceeding about 0.5% and with the balance essentially iridium.

6, Wrought iridium alloy sheet made of an alloy consisting essentially of about 0.1% to about 0.5% metal from the group consisting of about 0.1% to about 0.5%

titanium and about 0.1% to about 0.3% zirconium with the balance essentially iridium, said sheet being characterized when in the condition obtained by rolling at about 800 C. by an ultimate tensile strength of at least about 28 long tons per square inch at room temperature and a.

level of ductility suflicient to enable the sheet when about 0.02 inch thick to be bent around a radius of about three-eighths of an inch without cracking.

References Cited by the Examiner Titanium-Iridium Phase Diagram, Croeni et al., Bureau of Mines Report of Investigations, 6079, 1962, 15 pages.

DAVID L. RECK, Primary Examiner. H. F. SAITO, Assistant Examiner. 

1. AB IRIDIUM ALLOY CONSISTING ESSENTIALLY OF ABOUT 0.1% TO ABOUT 0.5% METAL FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WITH BALANCE ESSENTIALLY IRIDIUM. 